TIN

253

sodium sulphide is dissolved in a little nitric acid (D 1-2) and the solution
evaporated in presence of sulphuric acid until white fumes appear; the
residue is treated with water, alcohol added and the lead sulphate collected
on a closely-woven filter paper. As it may contain small quantities of
tin, the precipitate is redissolved in ammonium acetate solution and the
lead reprecipitated with hydrogen sulphide and converted into sulphate,
which is collected on a Gooch crucible as usual (see Gravimetric Determina-
tion of Lead in Ordinary Brass).

(b) DETERMINATION OF THE BISMUTH AND COPPER. The alcohol is
expelled from the liquid separated from the first lead sulphate precipitate
and the bismuth and copper precipitated with hydrogen sulphide and
determined as in the analysis of antimony.

(c] DETERMINATION OF THE IRON. The iron is determined as oxide
in the filtrate from the bismuth and copper sulphides (see Determination
of Iron in Antimony).

2. Determination of the Antimony.—10 grams of the sample are
treated with 100 c.c. of hydrochloric acid (D 1-124) an(i potassium chlorate,
the chlorine eliminated by boiling, the volume made up to about 250 c.c.,
and, while the liquid is heated on the water-bath, 6 grams of pure reduced
iron added in small quantities to displace the copper and antimony. The
separated metals, together with the small amount of undissolved iron,
are filtered off and washed on the filter with dilute hydrochloric acid until
the filtrate no longer gives the reaction for tin with mercuric chloride. The
separated metals are then dissolved in hydrochloric acid and potassium
chlorate, the excess of chlorine expelled by boiling, the copper and antimony
precipitated with hydrogen sulphide and the precipitate well washed and
treated with 30 c.c. of sodium sulphide solution (D 1-225) to dissolve the
antimony sulphide. The liquid is filtered directly into the Classen dish,
the filter washed with 50 c.c. of the sodium sulphide solution, and the filtrate,
with the addition of 5 -6 grams of potassium cyanide, electrolysed to deter-
mine the antimony (see Determination of Antimony in Hard Lead).

3. Determination of the Arsenic.—(a] 10 grams of the sample
are dissolved in a solution of 100 grams of ferric chloride in 100 c.c. of water,
excess of cone, hydrochloric acid being added and the arsenic distilled in
the ordinary way (see Determination of Arsenic in Iron).

(b) 10 grams of the sample are dissolved in hydrochloric acid contain-
ing potassium chlorate, the chlorine being expelled by boiling, and the
cold liquid mixed with one-third of its volume of cone, hydrochloric acid
and hydrogen sulphide passed through it for some hours. The arsenic
sulphide thus precipitated is filtered off on an asbestos filter (Gooch crucible),
washed with cone, hydrochloric acid and then with boiled water and dis-
solved in ammonia ; the solution is evaporated in a dish and the residue
dissolved in cone, nitric acid, made strongly alkaline with ammonia and
the arsenic precipitated with magnesia mixture and alcohol. The precipi-
tate is collected, washed, transformed into pyroarsenate and weighed.

4. Determination of the Sulphur.—See Determination of Sulphur in
Iron,

#**e being regarded—not always with